This invention relates to a method of correcting the error between an accelerator pedal position sensor and a throttle valve position sensor in a vehicle and an internal combustion engine where the throttle valve is controlled not only by the position of the accelerator pedal, but also by a means independent of the accelerator pedal.
A device which learns values output by a throttle valve position sensor of an internal combustion engine when the throttle valve is fully closed, and corrects the values output by the sensor based on the learned values so as to remove errors between the values output by the sensor and actual values of the throttle valve position, is disclosed for example in Japanese Provisional Patent Publication (Kokai) No. 56-107926.
In general, a throttle valve of an internal combustion engine for automotive vehicles is controlled by the accelerator pedal, but if the vehicle driving wheel or wheels slip due to the road conditions, the engine output must be temporarily reduced to eliminate the slip quickly. For this purpose, a traction control system (referred to hereinafter as TCS) is known in the art which controls the throttle valve to a smaller opening independently of the action of the accelerator pedal. With this system, the throttle valve normally rotates in a 1:1 correspondence with the action of the accelerator pedal, but when the driving wheel or wheels slip, a pulse motor drive connected to the throttle valve releases the valve from the accelerator pedal drive to rotate it by a predetermined amount toward the closed side.
The accelerator pedal and throttle valve are both provided with sensors that detect rotational angular position thereof. The difference between the values output by these to sensors is used to observe whether the accelerator pedal and throttle valve are moving with a 1:1 correspondence, as proposed e.g. by the assignee of the present application in Japanese Patent Application No. 2-119542, and to determine the initial position of the pulse motor (e.g. proposed by the assignee of the present application in Japanese Utility Model Application No. 2-31476).
However, if there are errors between the values output by the accelerator pedal angle sensor, throttle valve angle sensor and the respective actual angular positions of the accelerator pedal and throttle valve, and an error in the relative position of the accelerator pedal and throttle valve, the difference between the values output by the two sensors could be as much as the sum of the three errors. If the observation and determination are based on differences containing these errors, therefore, there is a risk that the performance of the vehicle and engine might deteriorate.
If the aforesaid conventional technique for correcting the output value of the throttle valve position sensor is applied to the above two angle sensors, the errors in their output values can be corrected. However, if the error in the difference between values output by the two angle sensors also contains elements due to a shift in the relative position of the accelerator pedal and throttle valve, a difference (relative error) corresponding to the shift appears in the output values of the two sensors even if the accelerator pedal and throttle valve are moving with a 1:1 correspondence, and a deterioration of the vehicle's performance is unavoidable.
Further, by the aforesaid conventional technique for correcting the output value of the throttle valve sensor, the sensor output value is learned when the throttle valve is fully closed, and sensor output values are corrected based on this learned value. In general, however, the error in the sensor output value varies with the opening of the throttle valve, and if the output value is corrected only on the basis of the value learned when the throttle is fully closed, the output value may not be correct for other throttle openings. Even if the conventional correction technique is applied to the above two angle sensors, therefore, the output values cannot be corrected over the whole range of throttle openings.